Dorei Tensei: Sono Dorei, Saikyou no Moto Ouji ni Tsuki
Slave Reincarnation ~ That Slave / is the Strongest Former Prince ~

Ars, the young ruler of the Kingdom of Karitz and a wizard known for his practical approach, faces death at an early age. Just before he dies, he uses resurrection magic and is reborn as Wals Sai, a slave with an exceptionally powerful body. Wals becomes the escort of a princess from a small country. With his new physical strength and magic, he takes on the enemies threatening her, emerging as a formidable slave.